Siphon break

[Bimini Babe 0]

OK crew.org Special Advisory Board... here's another one for ya...

 

I'm going to fit a siphon break in the exhaust water injection line on my shiny new motor. The manufacturer's 'recommended' anti siphon valve is the Vetus one that costs about $200+... (Man those guys at Vetus sure know how to make a killing on plastic!)

 

...but the guy at the chandlery reckons the cheap vented loops intended for toilets would be fine instead. D'ya think?

[Guest]

Is the guy in the chandlers gonna pay to fix your motor if he's wrong?

Do you have more come back if you fit the recommend item and then something goes wrong?

Which one comes in Pink?

[Steve Pope 243]

I have a syphon break which is simply a small tee (5mm outlet) into the water injection line that then vents through a piece of plastic tubeing into the cockpit. When the engine is running water dribbles out at low revs, the flow increasing as the revs go up. It gives you a visual grom the cockpit that all is well with the pump / impellor. When you stop the motor the small amount of water in the tube drains back into the exhaust pipe. Simple, easy to do, cheap.

[wheels 543]

(Man those guys at Vetus sure know how to make a killing on plastic!)

Urrr, yeip! I melted the silencer and got a heck of a shock with cost. I never replaced it. I thne melted the Lift box and got an even bigger shock. Never replaced it anbd all works fine.

As for the antisiphon, yes the toilet vented look is just fine. They are very reliable.

[shanson 0]

I've had one of those vented loops in Cetacea for about a year now with no problems!

 

SHANE

[Bimini Babe 0]

Sweet, thanks for the feedback guys. Now, off to look for a pink one...

[Absolution 7]

Since your engine is a new install I'd be checking with the folks that installed it so you don't cause a potential warranty issue.

[Bimini Babe 0]

To be honest I don't think there's technically any requirement for me to have a siphon break at all. The injection point is a few inches above the waterline. I'm just putting it in anyway to be soooooper safe.

[wheels 543]

The normal level of water while sitting upright is not the issue it is when it is heeled over that the water level may perhpas get to be below the engine level and that is when a siphone break is important.

are you saying one does not need a lift box or muffler setup- a long looped hose

That depends. Muffler is only for noise if there is any. The lift box or water box or Waterlock or whatever many call it, is there to lift the water out of the boat. It works by a pressure biuld up and you see this at the exhuast outlet. the water stops for a moment as the water has blocked the outlet in the liftbox and then as the exhaust pressure rises and overcomes the waters weight, the water suddenly shoots out with the extra exhaust pressure and the cycle starts again. This can lift water some 3 to 4 metres. It ensures the water is lifted over goosnecks and so on. Most boats need it. for mine, the exhaust is probably 8m long and is a 3" hose and the same thing actually happens with just the hose and goosneck. The water biulds up at the goosneck till the pressure overcomes and shoots up and over. I just happen to be lucky it works that way. I found out only after I made a temporary repair when I melted the plastic lift box. Figured darn it, why spend $600 for a plastic box. I was going to make a SST one and never bothered in the end. I do need and have one on the genset though.

[Guest]

But what happens to the water remaining in the looped pipe when you crank your engine?

[wheels 543]

Just like the water in the lift box, the exhaust pressure blows it out.

[Guest]

I must be dumb.

 

The volume of an exhaust system is far less without a muffler. So if cranking an engine repeatedly can cause water ingress through the exhaust manifold by flooding the exhaust system with raw water, without a manifold you will just stuff up your engine that much quicker.

[PaulR 3]

I must be dumb.

 

The volume of an exhaust system is far less without a muffler. So if cranking an engine repeatedly can cause water ingress through the exhaust manifold by flooding the exhaust system with raw water, without a manifold you will just stuff up your engine that much quicker.

 

Too tempting knot to reply. I think you mean waterbox instead of the 2nd manifold, where the cooling water exits the engine and mixes with the exhaust fumes before going through the water box / antisyphon / swan neck loop to skin fitting / over the side.

 

"It depends upon the angle of the dangle"

 

i.e. the drop / rise & fall from the engine to skin fitting and more importantly when the yacht is knocked down or heeled right over.

Exhausts exiting through the tansom seem alwaya a lot safer compared to yachts where the exhaust is in the aft quater of the hull.

 

I recommended one yacht fit a gate valve to the side skin fitting, but this did not happen, so the owner was later up for a complete new engine, because the sea water had been "pumped" through the exhaust into the engine during a blow when the exhaust was under water in large waves off the Northland coast.

[wheels 543]

There are as many set up's as there are boats and not all will suit not having a lift box. For mine...the engine is a biggy being a 6cyl, 354cubic inch perkins. There is a water cooled exhaust manifold and then a "hot" exhaust riser that stops water from the mixed exhaust/water getting back to the engine. The cooling water is mixed into the exhuast on the downside of that riser where it continues to drop another couple of feet down to where the liftbox once was. The exhaust then travels another 3m to the point of where the muffler once was. The exhaust then travels another 3m to the second riser or "goosneck" where it rises a good 1m and then down again to where it exits the stern. So outside Sea water can not get back up the exhaust and the riser at the engine stops water in the exhaust from entering the engine. At some stage when I get that far down my "to do list", I will biuld another lift box from SST. It is that for my install, it works OK without, so the item is not at the top of the "To do" list. For others, it could be an essential item and I certainly do not suggest everyone should remove their Lift box. For ver long installations, the muffler is also about stirring up the water and exhaust again and not just that it silences the exhaust. So once again, it is something I do not suggest being removed. The result on my boat is a "ballsy sounding" exhaust note of which many yachties do not want ofcourse. We don't here it unless you stick your head over the stern.

[PaulR 3]

Sweet, thanks for the feedback guys. Now, off to look for a pink one...

 

 

Just for the boys to know how much you love PINK!

Bimini Babe off to town for her pink one....

[Bimini Babe 0]

Can't be me though of course, everyone knows I'm a Kubota girl.

[Guest]

PaulR - I think you mean waterbox instead of the 2nd manifold, where the cooling water exits the engine and mixes with the exhaust fumes before going through the water box / antisyphon / swan neck loop to skin fitting / over the side.

 

Of course……to much editing/cut and paste/etc.

 

My point is the volume of water required to fill up the exhaust from cranking the engine that leads to water in the engine.

 

Cheers

[wheels 543]

Providing your exhaust is designed correctly, Overflowing an exhaust back to an engine via cranking takes a lot of water and thus a lot of cranking and that would mean you have an engine problem. In which then you would shut off the water intake till the eninge problem is solved and then open again before engine is fully started.

The muffler adds very little volume to your exhaust, if any at all. The liftbox adds a little, but not a lot. Maybe a cup or two. Most of the liftbox is empty and is there to act as a "bellow" to pulse the water up and out of the exhaust.

In my case, the volume of 6m by 75mm of exhaust is one hell of a lot of water before it ever got back to the engine.

[PaulR 3]

Been in a situation where a Volvo (MD2??) that had a max rpm under 4,000, was screaming at over 7,000 rpm and more , , , needed a book over the air intake to kill it. NEVER use your hand!!

 

ScreaMMMMMMMMMMMing it was. Thought bits were about to fly everywhere, and got out of cockpit quickly.

 

It was caused by sea water somehow getting into the clyinders and we were running on a fuel/water mixture.

 

Even going in reverse failed to drop the revs!!

 

So how the water got there was a mystery. I don't now if there was a leak in the clyinder walls or knot, but it could also have been water up the exhaust during a Southerly Buster blow west of Bass Strait, the previous day.

 

So a gate valve on the exhaust is what I recommend, especially offshore. Easy to leave open for most use, but hard to fit one at sea in a storm if you want or need to close off.

[wheels 543]

It was caused by sea water somehow getting into the clyinders and we were running on a fuel/water mixture.

Errr, nope, water won't cause that. A broken govenor is what causes that and it is scary as anything to hear a Diesel go into runaway. They sound like a bag of hammers thrown into a jet engine. I have seen a big tractor do that and it stretched the headbolts lifting the head off the block and bent all the conrods and push rods. The blacksmoke was something else, but the noise was unbelievable.

Re the water in a diesel, it is a killer in two ways. One is it takes a drop to rob the cyclinder of enough heat to produce combustion. If the engine is already running, then it only takes a teaspoon of water and there is not enough gap between the piston head and the cylinder head and the result is a hydrauliced engine. And i have seen a Diesel that had cracked the Block when it was dunked.